WARNING: The following contains spoilers for Attack on Titan Season 4, Episode 27, "Retrospective," now streaming on Funimation, Hulu and Crunchyroll.
Former protagonist Eren Jaeger has done some pretty terrible things in the Final Season of Attack on Titan. After launching a sneak attack that killed innocent civilians in Marley and overthrowing the military on Paradis Island, he went full villain by activating the Rumbling to wipe out all life on Earth. Eren's intended genocide of the human race undeniably makes him an irredeemable character -- but the Rumbling isn't the only one of Eren's sins that is wholly unforgivable. Eren has brought unimaginable suffering upon his closest friends by forcing them to kill their own comrades just to stop him.
The Scouts and Marleyans who've joined forces to stop the Rumbling have the most reasonable, frankly undebatable, opinion in the history of anime: genocide is wrong. Eren's plan to wipe out all life beyond Paradis Island is unjustifiable even in the face of the rest of the world's hatred for Eldians. Yes, Eren and the Jaegerists are correct that the rest of the world would just as soon wipe out the Eldian race, but a preemptive genocide to prevent genocide is still genocide. So, despite the fact that the Marleyans and Scouts who've teamed up represent the minority opinion on Paradis Island regarding the Rumbling, stopping Eren isn't just the right thing to do -- it's the only thing to do.
That Eren would activate the Rumbling at all is terrible, but even without the omniscient power of the Founding Titan, he must have known his friends wouldn’t be on board with his plan. If he thought they'd support him, he would have included them from the start instead of Floch Forster. Yet Eren abandoned his friends, forced them to come save him in Marley, then imprisoned them while he overthrew their own military -- all the while knowing they would feel responsible for his actions and try to stop him. In Season 4, Episode 27, "Retrospective," Hange, Mikasa, Connie and Jean slaughtered dozens of Jaegerists, their former comrades, and it is entirely Eren's fault.
Connie's horror at having to execute Samuel and Daz, people he's known since their days in the 104th Cadet Corps, is just a taste of the psychological torture Eren has inflicted upon the people he once claimed to care most. It’s a simple concept that if you love someone, you don't force them to murder their own friends so they can stop you from destroying the world. Eren proclaims to be acting on behalf of the people of Paradis Island, but he's actually the most selfish character in Attack on Titan. Eren has suffered tremendously in the war with Marley, and now he's going to let his pain roll over the Earth while devastating those closest to him.
To be fair, the Jaegerists made their choice by following Eren's genocidal plan, but Eren is the one who radicalized his followers in the first place. By recruiting Floch Forster to be the head of the Jaegerist faction, Eren ensured that they would be xenophobic extremists under the leadership of a man who once tried to spare Erwin Smith's life only so he would live long enough to keep suffering. Floch has gone from a hot-head to a patriot, to a borderline psychopath as a result of feeling like the prodigal son as Eren's righthand man in the plot to destroy the world.
Just as the Scouts have been forced to kill their own comrades, the Jaegerists are just as distraught to have to fight their former allies who've betrayed them. Paradis Island has become a madhouse thanks to Eren, and even if he's stopped or convinced of the error of his ways, his character is beyond redemption. Every drop of blood spilled in the clash between the Scouts and the Jaegerists is on Eren's hands, and his friends may never be the same again for having killed so many of their own comrades. Eren Jaeger created Attack on Titan's ultimate mess and left his friends to clean it up. Mikasa and the others will want to be merciful to Eren when they catch up to him, but he sure doesn't deserve it.
